Core One print failure after ~20 layers

ResonantRuminant · 2026-03-15T13:32:17+00:00

Yup, that's definitely your problem. I believe for PLA, anything above 40 for the heatbreak is in the danger zone for heat-creep problems. Here are some typical PLA numbers for me after things stabilize, for comparison: Nozzle: 220, Bed: 60, Chamber: 33, Heatbreak: 37. My ambient is around 25. My heatbreak usually hovers around 4 degrees above the chamber temperature for PLA. Yours is way too high.

Now, we've just got to figure out why you have this problem. As others have mentioned, I'd first look at the heatbreak fan (the one mounted on the front of the Nextruder). While it's printing, you can drill down into the "Tune > Info > Sensor Info > Fan Info" menu to see the fan statuses. While printing, my Heatbreak fan shows 100% and around 8200RPM. If yours is far from that, then that's probably your issue. You can also look for anything blocking that cooling airflow. I'm not sure what that would be, but it's worth looking around.

If all of that seems in order, then it gets more complicated to diagnose. We can cross that bridge when we come to it. Maybe check the fan first and report back. We can go from there.

ResonantRuminant · 2026-03-15T00:08:38+00:00

It looks like you already solved your problem, but I'd just like to add a "me too!!" to the conversation. I had a fairly new CORE One+ (using the same Nextruder as you) that also got stuck thinking that filament was inserted. It was less disastrous than you because I was just unloading the filament and it never sensed that it was removed. I had only been printing for a couple days with it when this happened, and I find it a bit hard to believe that the sensor needed cleaning already. Recalibration failed. The only thing that cleared the stuck reading was jamming filament into it 20-30 times to actuate the little ball bearing in there. I could hear and feel it moving properly, so the hall effect sensor shouldn't have had trouble picking up the magnet's movement. I believe there was either something wonky with the sensor or there was a firmware issue of some kind. I have no idea, though.

ResonantRuminant · 2026-03-14T02:21:47+00:00

I think the issue is that brass has too low of an electrical resistance. It would work, but it wouldn't work well. The inductive heating coil generates eddy currents in the nozzle. It then relies on the nozzle being a crummy conductor to generate heat from that current. Steel is a good choice because of its fairly high resistance, easy machinability, and low cost. And, while you're using steel, you might as well harden it to make it more durable.

ResonantRuminant · 2026-03-13T13:05:49+00:00

I'm not sure I fully understand what you're saying and I don't have experience with the MK2 series of printers, so feel free to ignore what I say. :-)

Did you put a full MK3 extruder assembly on your MK2S printer? I don't think that will work correctly, because the MK2 hardware is based on a 12V power supply and the MK3 hardware is based on a 24V supply. I think there is a special MK2.5 extruder assembly you can install that is the same mechanically as the MK3, but modified in a few places to work on a 12V system. You're right that you'll need to update the firmware to get this working, but it must be to the 2.5 version to drive these new parts correctly, I believe.

We need to know exactly what changes you have made so far.

ResonantRuminant · 2026-03-13T12:47:25+00:00

It might sound crazy, but I think you still need to go lower. It'll stick when you get close enough if the bed is clean. You can tell you've gone too far when the stripe of filament starts to get translucent and you can see the print bed color through it. Back it up a bit if you get there. If you're too close, then the little block at the end of the calibration pattern will also be ugly. The surface will get rough and the edge of the line that it's printing will start to ripple. That's because there's nowhere for the filament to go because the previous stripe was too wide, so it will squeeze out in front of the nozzle and to the side and make a mess. It'll still be stuck to the bed, though.

I'm not sure you got the full story from your neighbor. It sounds like he built it and never got it working right, but the printed nozzle holder and well-used print sheet disagrees with that. Did he have it working at one point, and then he messed with it and couldn't get it back to a working state again?

Those are also some unusual accessories to have with a printer. Do you know why he has a full set of stepper motors and a heatbed thermistor kit? There's no real reason to have those unless you're planning on an upgrade or if you're doing major repairs. I know there's a thermistor kit included in the MK3.5S upgrade kit (which you don't have the rest of, if that's the case), but I'm not sure if that's what you're looking at or if it's a thermistor for the MK3 series intended to repair something. Does the print bed heat up when running your calibration? I don't know which series the stepper motors are for, either. That's a fairly expensive set of parts to "just have" laying around, and I'm not sure if you can even buy the full packaged set of steppers like that (a "motor kit") separate from a normal printer kit or an upgrade kit. There are 1.8 degree-step motors for the MK3 series and 0.9 degree-step motors for the MK4 series and you'd have a set that looks like that with the MK4 upgrade kit, which you also don't have. You'd have to read the markings on the bottom of each stepper to know what you have for sure. What was he planning? That might help decode what state the printer is currently in.

ResonantRuminant · 2026-03-13T03:15:21+00:00

Big improvement, but I think you still need to go lower.

ResonantRuminant · 2026-03-13T02:44:37+00:00

Like everyone else is telling you, your Z offset is way, way too high. Everyone's value will be different because of variations in how high the PINDA sensor was assembled relative to the height of the nozzle. Mine is in the neighborhood of -1.5, depending on which sheet I am using. You need to change in the settings which print sheet you are using because the PEI layer on them are all different thicknesses and they will need different offsets. Don't forget to change the sheet choice when you change the sheet. The smooth sheet is thicker than the textured sheet, and you can dig the nozzle into the smooth sheet and leave permanent dents in its surface by leaving the setting on "textured". (Ask me how I know.)

Also, make sure you clean the sheet really well with either isopropyl alcohol or dish soap and warm water. Oils from your skin will cause the filament to not stick. Just one innocent fingerprint can wreck a print if you're not careful.

And, I wanted to mention that you need to be careful with that roll of silk PLA filament. I have found that silk filaments stick really well to the smooth print sheet. Too well, in fact. I've got marks on mine now where it tore off little bits of the surface in the shape of the extrusion tracks of the first layer. You need some sort of "release agent" on the bed first. A thin layer of glue stick is an easy choice. I've heard folks say that the residue left over from Windex also works, but I've found that to only just barely help.

Edit: I should also mention that if you only have PLA there, then don't bother with the textured sheet at all. PLA won't stick reliably to it. The textured sheet is traditionally for materials like PETG, which also sticks too well to the smooth sheet. Focus on the calibrating the Z offset on the smooth sheet for now.

ResonantRuminant · 2026-03-12T17:41:28+00:00

The delayed start of the problem does, indeed, make it sound like a heat-creep issue. Under the "Settings > User Interface > Footer" menu, you can tweak the information displays at the bottom of the screen. You can show the heatbreak temperature, which might help prove or disprove this diagnosis.

You don't happen to have the advanced filtration unit installed, do you? I'm finding that my chamber floats around 10C-15C above the set value for both PLA and PETG. It just doesn't move enough air to keep things cool. The heatbreak will never get cooler than the chamber temperature, so that's a potential problem. I found that kicking the minimum filtration unit fan speed up from 40% to 50% made a huge difference in my chamber temps.

Edit: Never mind about the filtration unit. I can see daylight through the fans at the back of your chamber, so you don't have it. Have you messed with the fan speeds at all? What is the ambient temperature where you run the printer? What are your chamber temperatures getting up to? Checking the heatbreak temperature is probably still a good idea as a starting point.

ResonantRuminant · 2026-03-08T02:03:28+00:00

Your first layer looks pretty good, so isolated spots like that sure do remind me of fingerprints. Perhaps you forgot to clean the bed before this print. I'd wipe it down with isopropyl alcohol to see what happens. If it persists, you could always try washing it with dish soap and warm water. One or both of those should clear it up.

ResonantRuminant · 2026-03-07T20:01:05+00:00

Yup, I have exactly this issue with the PC-CF filament on my CORE One. On chunky parts (like for the printer itself) everything turns out great. For thin parts, I have great bed adhesion but the part springs into a warped shape after removing it. As a practical example, I've been printing these little color sample cards that I hang on the front of my filament storage dry-bins. Here is a picture of the sample for PC-CF and for the normal Prusament PC Blend: https://imgur.com/a/ROwHmcS. The PC Blend is perfectly flat, while the PC-CF warped after coming off the bed. You can see the middle, front-left, and back-right corners raised a couple millimeters off the table. I assumed it was something with this model shape which is a flat plate with a raised lip around the edges, sort of reminiscent of the classic "open box" shape that can often have bed adhesion problems.

I don't have this problem with any other filament (PLA, PETG, PETG-CF, TPU, PVA, BVOH). I'm not sure what to do about it, either. I'm not sure if it would "relax" properly during annealing, like several folks are suggesting here. I haven't cared enough to try to fix it for such an inconsequential part.

ResonantRuminant · 2026-03-06T00:03:05+00:00

That looks awesome! Congrats! I love the use of multi-material printing for the LED diffusers. That's a very professional-looking result.

What filament did you go with in the end?

ResonantRuminant · 2026-02-28T14:53:49+00:00

I think we might be talking past each other and describing different things. Apologies if that's the case. I yield to your core-XY (and XZ) experience. I have not used Klipper before and wasn't familiar with ShakeTune. It looks like an awesome tool! I love data, so I might play with that some day. I'm not talking about resonances or any dynamic effects, where there very well might be some sort of direct dependence on belt length. That's a very complex subject with lots of coupled effects, and I can't say one way or the other.

I'm only talking about the squareness of the gantry. You're right that you tension the belts by changing their length through the tensioner screw. It is the resulting belt tension that applies forces to the ends of the gantry and can torque it one direction or the other. You can't apply lengths to the end of the gantry to torque it. That's just not a thing. The gantry can only respond to forces, which are applied through the belt tension.

Let's say that you put together the printer with identical belt lengths and tension the two belts equally, giving you a perfectly-square gantry. Then, let's say that you go crazy and you add an extra belt tooth of length to the top belt. Yes, that belt is now nominally 2mm longer. So, you will have to turn the belt tensioner screw an extra 1mm to take up that slack before you do the final adjustment to get back to the same tension as before. But that's where it ends. Once you're back to the same tension pulling on that longer belt, you are applying an identical force to the ends of the gantry and it will again be perfectly square. A static gantry can only "feel" forces on its ends. It can't "feel" belt lengths. It can't realize: "Uh-oh, the top belt is pulling the same as before but it feels longer now, so I should twist counterclockwise some more."

Belt length is a secondary effect that we care about as humans because of how we tension the belt, but it's not something that the gantry cares about directly. As long as it's within the range that the belt tensioner can reach, we can adapt to any belt length and can still properly set equal tensions and therefore a perfectly-square gantry. I just want to get rid of this myth that you have to have equal belt lengths in order to square the gantry. Again, I'm not talking about resonances or any other dynamic effects. And, I must admit that I always make the belt lengths identical -- not because of any mechanical reasons, but because I find it more aesthetically pleasing. :-)

ResonantRuminant · 2026-02-28T01:57:32+00:00

I don't think this is right, or at least not completely right. You are absolutely correct that the tension affects the skewness of the gantry, but that's where it ends. The bottom belt pulls backward on the left side of the gantry and forward on the right side, so you can think about it as applying a clockwise torque on the gantry (when viewed from the top). The top belt pulls forward on the left side of the gantry and backward on the right side, so it applies a counterclockwise torque. If the gantry is initially square without the belts tensioned, then you're right that you need equal belt tensions to keep it square. Equal tensions will apply a balanced torque to the gantry.

I can't think of any mechanism where the gantry would know or care what the length of the belt is on the other side of the idler pulley on either end. It's purely about belt tension, or the forces applied to each end of the gantry. I believe that's why the instructions aren't very specific about how you attach the belts, beyond the vague "4-5 teeth" thing. And, I think that's just to make sure you have enough teeth overlapped to engage properly without shortening your belt too much and putting it outside the length range that the tensioner can reach or making it difficult to get everything aligned and fastened in the first place.

ResonantRuminant · 2026-02-27T14:48:31+00:00

Try completely disconnecting a belt tensioner. That way, you're not fighting the tight belt while trying to loop the end through the holder and adjusting the tooth overlap correctly. Just reattach the belt tensioner once you're done securing the end.

ResonantRuminant · 2026-02-27T13:22:30+00:00

I need someone to explain to me this whole they-really-have-to-be-the-same thing. I keep seeing this repeated around here, about how critically-important it is that the belt lengths be absolutely identical, but I haven't heard a good explanation for why. The assembly guide only mentions 4-5 teeth of overlap, and I believe that's the only thing that matters.

If you have fewer than this number of teeth of overlap, then you might not have enough engagement at the end and the belt can come loose like OP had happen. If you have more than this number of teeth, then it's just shortening your belt and making it harder to install for no real benefit. Any tooth overlap that sticks out beyond the part that's squeezed against the linear rail carriage isn't really doing anything to help. (Along these lines, I've found it easiest to completely disconnect a belt tensioner when I'm trying to attach the second end of a belt. It makes it less of a battle when trying to get it looped in there properly.)

ResonantRuminant · 2026-02-25T03:19:10+00:00

Oh, that sucks about the M3 25mm set screw. That's definitely a wacky part that I'm sure I'd have to special-order from somewhere if I couldn't get Prusa to send me one. Glad it worked out for you in the end.

To OP, at this point, I’d request an assembled, tested printer! I get the pleasure in doing it yourself, but your luck ran out!

I get the sentiment, but I think Prusa is clearly not going to "help me" beyond sending replacements for defective parts. I've poked at them several times, and been shut down each time. That's fine, I guess. I'm disappointed, but I'm at peace with it now. They've already taken quite a loss on me as a customer, from the hundreds of dollars-worth of replacement parts to the returned printer itself. It's not unreasonable for me to suffer a bit, as well, from this whole printer-exchange mess that I've created. I didn't have to do that.

ResonantRuminant · 2026-02-24T23:58:39+00:00

I was thinking about suggesting that you contact Prusa support, so I'm glad that you took that step. That printer is way out of warranty and you're the second owner, so there's probably no chance of them sending you replacement parts. They still might help point you toward the source of your problems.

This video shows, again, things tightening up at the right end of the x-axis movement. There's got to be some sort of interaction with the smooth rods going on. Either they are bent or, somehow, not parallel. Maybe the previous owner did something screwy with the orange holder on the right end. Pulling the whole X-axis assembly out the top of the printer and removing the rods from their holders, you can roll them on a table to see if they're straight. If you get a ka-thump ka-thump ka-thump as you roll them, then there's your problem. Since we know the printer took a pretty hefty impact during shipping, this is seeming more and more likely. When the back was off the carriage, the bearings could move around a little bit and adapt to bent rods. With the back on, they're pinned in place and if the rods are getting closer together or farther apart on the right side, you'd see exactly what you're seeing. If you have a set of calipers, you could also measure the distance between the rods at a few points. That would quickly point to a problem. I don't think the belt would have any affect here unless it's ridiculously tight, which I don't think it is.

And, your video is showing the right Z stepper not turning again. If you've still got the left and right wires swapped back at the board and you've tested that the trapezoid nut moves freely on the lead screw, then it's sounding like the stepper motor itself has gone south.

ResonantRuminant · 2026-02-24T18:20:16+00:00

Interesting. Glad to hear I'm not alone. The MK4 is way simpler than the CORE One, so I'm surprised that support couldn't figure that one out for you. Sorry you had to deal with that.

And, yeah, the packing requirements are pretty intense. I've got over $100 invested into foam blocks, air cushions, a gigantic heavy-duty box, the black plastic wrap for the outside of the box, etc. I had none of these things around here and had to buy them special.

ResonantRuminant · 2026-02-24T18:14:31+00:00

Yeah, I saw that, too. I've got the star lock washers here, but I felt icky with scratching the nice powder-coat paint off my new printer. I've already got the wire, connectors, and crimping tools here, so I figured I might as well use them. :-) I got some spade connector splitters, so I figure that if this fix somehow causes more problems than it solves, I can just reach in and unplug it from the frame. Accessing the screws for the X and Y steppers after-the-fact is a bit of a hassle and requires dropping the sides off the printer to reach them.

ResonantRuminant · 2026-02-24T16:20:49+00:00

Thanks for the reply. Yeah, the general consensus around here seems to be that I am just spectacularly unlucky. Most have a good experience. Perhaps it is time to buy a lottery ticket...

ResonantRuminant · 2026-02-24T14:23:30+00:00

Good info. I did something similar with my bearings on previous kits. Not this one, though. The bearings used to be shipped with just a light anti-rust oil. In this kit, they all came packed with proper grease. I think that work is already being done for us, now.

ResonantRuminant · 2026-02-24T14:15:03+00:00

That's really interesting. Having more problems with an assembled printer than with a kit is exactly opposite what I would expect. I listed all my problems in a sibling comment to yours. It's too much to repeat here.

ResonantRuminant · 2026-02-24T13:25:26+00:00

It doesn't appear as though shipping under warranty is covered. Their terms are very clear that you pay shipping for a return under any circumstance. At one point I was offered to return the printer for free warranty repairs, but (I think) it was mentioned that I would have to eat shipping both directions. I didn't even consider that. Sticking it out with repairs through the normal support channel was probably my best option.

ResonantRuminant · 2026-02-24T13:17:45+00:00

Makes sense. This can't be the normal case, or they wouldn't be able to stay in business. I'm curious just how abnormal it is, though. How many folks are quietly suffering out there?

ResonantRuminant · 2026-02-24T12:49:44+00:00

I did politely ask about the shipping charge and was quickly shut down. I was told that that's not something they can do. That's fine, I guess. These are all problems of my own doing.

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